VBA loop to delete entire row if cells contain a particular string

I need code to go through cells of a column of unknown length and delete the entire row if the cells contain a particular string ("--"). This is what I have so far, but it does not work. Can anyone help? I can't program.

Dim RowKdx As Long For RowKdx = Range("b1").End(xlDown).Row To 2 Step -1 Do While Cells(RowKdx, "b").Value <> "" If InStr(RowKdx, "--") = 1 Then Rows(RowKdx).Delete End If RowKdx = RowKdx - 1 If RowKdx = 1 Then Exit For Loop Next RowKdx